Depends - the default constraint is GETDATE(). Does the EventOn column actually need the time of day?
If it doesn't, and you always rely on the default to enter the date for EventOn, change the default constraint so it returns the date at 0:00:
DATEADD(DAY, DATEDIFF(DAY,GETDATE(), 0), 0)
Memory isn't too clear right now - could be this as well:
DATEADD(DAY, 0, DATEDIFF(DAY,GETDATE(), 0))
... make that:
DATEADD(DAY, DATEDIFF(DAY, 0, GETDATE()), 0)

Just throwing in some more ideas:
-You could use a computed column on the expression Adriaan gave, persist it, and put an index on it.
- Leave it as it is and derive the date-only information at runtime of a query.
What do you want to use it for?